During the manufacture of certain types of printed circuits, particularly electroless-plated printed circuits, an insulating surface of a substrate is first coated with a treating solution and then heated in an oven to form a thin solid film of coating on the substrate surface. Selected portions of the dired coating are then exposed to ultraviolet light through a glass art master, or mask, to delineate catalytic metal deposition sites at the exposed areas. The glass art master has located on one of its surfaces darkened land areas, or opaque sections, representing the outline of the circuit which is to be exposed onto the substrate by the ultra-violet light, and it is essential that each substrate be properly aligned with the surface of the glass art master to insure that the circuit is exactly placed on the substrate during exposure. To assure that the substrate is properly aligned, a typical glass art master has two steel registration pins located at diametrically opposite corners of the art master, with a lower portion of each pin embedded in the glass and an upper portion extending above the surface of the glass. Each printed circuit substrate has two registration holes located such that when the holes are placed over and fit onto the upper portions of the pins, the substrate is properly aligned on the glass art master.
Because the glass art master is typically made of heavy glass to allow for handling in a manufacturing environment and to prevent breaking, the weight of the glass and the substrate often combine to produce excessive shearing forces on the registration pins embedded in the glass thereby causing the glass around the lower sections of the embedded registration pins to crack. As can be realized, any cracking in the glass ruins the glass art master since the cracks will have the same effect as the opaque land areas and cause improper circuit configurations to be exposed onto a substrate during ultra-violet treatment. Furthermore, since the cracked glass can no longer firmly hold the registration pin in an exact position, the substrate positioned on the glass art master may not be properly aligned.
Therefore there is a need for a registration pin which will not crack the glass in a glass art master regardless of the forces applied to the pin.